It is now well-known that the comfort of a shoe is linked not only to correct anatomical contouring of the fit but also to correct outward permeation of the water vapor that forms within the shoe due to perspiration.
Traditionally, vapor-permeable shoes are those which use natural materials such as leather or equivalent products, which however, in the presence of rain or bad weather, indeed because of their vapor-permeable properties, do not ensure good waterproofing and indeed rather easily absorb water.
For this reason, shoes with an upper made of leather (or the like) coupled to a lining with a vapor-permeable and waterproof membrane (made for example of a material such as Gore-Tex® or the like), sewn or glued to an insole, have now been used for some years.
In the manufacture of such shoes it is important to pay attention to the sealing of the regions connecting the insole and the lining to the membrane and the sole, in order to prevent even the smallest infiltration of water from outside.
However, as is known, most of the perspiration of the foot is generated at the interface between the sole of the foot and the sole of the shoe, which is typically made of polymeric material.
It is evident that the perspiration that forms on this interface is unable to evaporate, condensing therefore on the plantar insert on which the foot rests; only a minor percentage of the perspiration evaporates through the upper.
For this reason, shoes have now been devised for years which are provided with vapor-permeable and waterproof soles (such as for example the one disclosed in EP0858270) which are associated with waterproof and vapor-permeable uppers, such as the ones described above, in order to provide shoes which are completely waterproof and vapor-permeable.
The shoe disclosed in EP0858270 in practice has a sole which is constituted by two layers with through holes and with the interposition of a membrane which is waterproof and vapor-permeable (made for example of a material such as Gore-Tex® or the like), which is joined perimetrically and hermetically to the two layers, so as to prevent water infiltrations.
This sole ensures correct vapor permeation as well as an effective exchange of heat and water vapor between the environment inside the shoe and the outside environment, at the same time ensuring the necessary impermeableness with respect to external humidity and water, in a manner similar to what is provided by the upper with which the membrane is associated.
In this shoe configuration, the sole and the upper are two separate parts, both of which are vapor-permeable and waterproof and are associated and sealed together so as to prevent the rise of water in the connecting points.
The soles used in such shoes are therefore structured so as to allow vapor permeation but not the flow of water from the outside inwardly; the structure of the sole is therefore more complicated than a traditional sole, and this complexity arises from the accommodation of the membrane and from the correct parametric seal thereof with the sole.
The same Applicant is studying completely waterproof shoes in which the vapor-permeable and waterproof membrane related to the vapor permeation of the sole of the foot is provided substantially monolithically with the membrane associated with the upper.
The idea is to provide a shoe composed of a lower part, which comprises a sole provided with through perforations from the tread toward the foot supporting region, and an upper pouch-like part, which surrounds the foot completely and is constituted by an internal pouch-like lining, with which a vapor-permeable and waterproof membrane is associated as an outer layer thereof and with which an outer vapor-permeable upper, closed in a downward region by an assembly insole sewn or glued to the upper, is laterally associated.
The sole is sewn or glued to the upper and to the assembly insole preferably with the interposition of a protective layer for the membrane.
This type of shoe construction, however, suffers drawbacks, due mainly to the fact that the water that rises from the holes of the tread and flows toward the inside of the shoe reaches the protective layer and the insole.
In particular, the insole becomes wet and transfers humidity also to the peripheral part of the upper to which it is fixed; such shoe parts, therefore, remain wet, and although the membrane prevents the water from entering the shoe, the foot receives an unpleasant feeling of damp cold.
Moreover, the parts impregnated with water in the long term may form colonies of molds, fungi and bacteria, which can produce unpleasant smells, leading to a general deterioration of the shoe.